Boat for heat treatment and vertical heat treatment equipment

ABSTRACT

The present invention is a boat for a thermal process including: a plurality of pillars; a plurality of claws formed in each of the pillars in a height direction at predetermined intervals; a plurality of supporting plates mounted in a tier-like manner between the plurality of pillars via the claws, each supporting plate having an object-to-be-processed mounting surface on which an object to be processed can be mounted; and a groove and a through hole provided in the object-to-be-processed mounting surface. According to the present invention, the groove and the through hole provided in the object-to-be-processed mounting surface form an air layer between the object-to-be-processed mounting surface of the supporting plate and the object to be processed, so that sticking of the object to be processed can be inhibited. Thus, even during a thermal process at a high temperature, generation of slip caused by the sticking of the object to be processed can be inhibited.

FIELD OF THE INVENTION

The present invention relates to a boat for a thermal process and avertical thermal processing unit.

DESCRIPTION OF THE RELATED ART

In a manufacturing process of a semiconductor device, there is a step ofconducting various thermal processes such as an oxidation process, adiffusion process, a CVD process, an annealing process, or the like, toan object to be processed, such as a semiconductor wafer. As a thermalprocessing unit for carrying out the step, a vertical thermal processingunit has been used, which is capable of thermally processing a largenumber of wafers at the same time. In the vertical thermal processingunit, a boat for a thermal process has been used, on which the largenumber of wafers are mounted.

As the boat for a thermal process, a ring boat that can supportperipheral portions of the wafers by circular supporting plates thereofhas been proposed (for example, JP Laid-Open No. 9-237781). In the case,slip (crystal defect) caused by gravity stress, which tends to beincreased by wafer enlargement (for example, 300 mm in diameter), can bereduced. In addition, thermal capacity of a peripheral portion of awafer, in which a heating and cooling rate is higher than that in acentral portion thereof, is so increased that uniformity of the processwithin a surface may be enhanced.

Herein, in the above boat for a thermal process, if the surface of asupporting plate has a minute irregularity or projection, the reversesurface of a wafer may be damaged or slip by gravity stress may begenerated more easily in the wafer. On the other hand, if the surfacesof the supporting plates are mirror ground in order to solve the aboveproblems, the wafers tend to be undesirably stuck to the surfaces of thesupporting plates. Thus, it is preferable that the surfaces of thesupporting plates are made a little rough by mean of a sand blastingmethod or the like, after the surfaces of the supporting plates areground.

However, in the case of the above boat for a thermal process, when thewafers are thermally processed at a high temperature of for example1050° C. to 1200° C., sticking phenomenon of the wafers to the surfacesof the supporting plates may be generated. In addition, because of thesticking phenomenon and minute irregularities or projections on thesurfaces of the supporting plates, slip by gravity stress may begenerated partly in the wafers.

SUMMARY OF THE INVENTION

This invention is developed by focusing the aforementioned problems. Anobject of the present invention is to provide a boat for a thermalprocess and a vertical thermal processing unit that can inhibitgeneration of slip in an object to be processed during a thermal processat a high temperature.

The present invention is a boat for a thermal process comprising: aplurality of pillars; a plurality of claws formed in each of the pillarsin a height direction at predetermined intervals; a plurality ofsupporting plates mounted in a tier-like manner between the plurality ofpillars via the claws, each supporting plate having anobject-to-be-processed mounting surface on which an object to beprocessed can be mounted; and a groove and a through hole provided inthe object-to-be-processed mounting surface.

According to the present invention, the groove and the through holeprovided in the object-to-be-processed mounting surface form an airlayer between the object-to-be-processed mounting surface of thesupporting plate and the object to be processed, so that sticking of theobject to be processed can be inhibited. Thus, even during a thermalprocess at a high temperature, generation of slip caused by the stickingof the object to be processed can be inhibited.

Preferably, a minute irregularity is provided in theobject-to-be-processed mounting surface in order to inhibit sticking ofthe object to be processed. In the case, the effect of inhibiting thesticking of the object to be processed can be increased.

In general, the object to be processed is substantially circular. Thus,it is preferable that the supporting plates are substantially circular,and that the plurality of pillars are arranged behind, on the left handof, and on the right hand of the supporting plates, perpendicularly tothe supporting plates. In the case, the object to be processed can beeasily mounted and removed away.

In addition, preferably, the supporting plate has a left engaging partthat can be engaged with a claw of the pillar on the left hand of thesupporting plates in order to prevent dropping of the supporting plate,and a right engaging part that can be engaged with a claw of the pillaron the right hand of the supporting plates in order to prevent thedropping of the supporting plate. In the case, the dropping of thesupporting plate caused by vibration or the like can be prevented.

For example, each of the left engaging part and the right engaging partis a stopper member that is abutted against a lateral wall part of theclaw.

Alternatively, preferably, the supporting plate has a left engaging holethat can be engaged with an upper portion of a claw of the pillar on theleft hand of the supporting plates, a right engaging hole that can beengaged with an upper portion of a claw of the pillar on the right handof the supporting plates, and a back engaging hole that can be engagedwith an upper portion of a claw of the pillar behind the supportingplates. In the case too, the dropping of the supporting plate caused byvibration or the like can be prevented.

In addition, preferably, dummy plates are mounted at an upper endportion and a lower end portion of the pillars. Specifically,preferably, a plurality of dummy plates is mounted in a tier-like mannerbetween the plurality of pillars via the claws, at an upper end portionand a lower end portion of the pillars, respectively.

In general, the object to be processed is substantially circular. Thus,it is preferable that the dummy plates are substantially circular, andthat the plurality of pillars are arranged behind, on the left hand of,and on the right hand of the dummy plates, perpendicularly to the dummyplates.

Then, preferably, the dummy plate has a dummy-plate left engaging partthat can be engaged with a claw of the pillar on the left hand of thedummy plates in order to prevent dropping of the dummy plate, and adummy-plate right engaging part that can be engaged with a claw of thepillar on the right hand of the dummy plates in order to preventdropping of the dummy plate. In the case, the dropping of the dummyplate caused by vibration or the like can be prevented.

For example, each of the dummy-plate left engaging part and thedummy-plate right engaging part is a stopper member that is abuttedagainst a lateral wall part of the claw.

Alternatively, preferably, the dummy plate has a dummy-plate leftengaging hole that can be engaged with an upper portion of a claw of thepillar on the left hand of the dummy plates, a dummy-plate rightengaging hole that can be engaged with an upper portion of a claw of thepillar on the right hand of the dummy plates, and a dummy-plate backengaging hole that can be engaged with an upper portion of a claw of thepillar behind the dummy plates. In the case too, the dropping of thedummy plate caused by vibration or the like can be prevented.

In addition, the present invention is a vertical thermal processing unitcomprising: a boat for a thermal process including the above feature;and a thermal processing furnace that can contain the boat for a thermalprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a vertical thermal processing unitaccording to an embodiment of the present invention;

FIG. 2 is a view showing a boat body of a boat for a thermal process,(a) being a plan view, (b) being a longitudinal sectional view takenalong an A-A line of (a);

FIG. 3 is a transversal sectional view showing a supporting-plateportion of a boat for a thermal process;

FIG. 4 is an enlarged sectional view taken along a B-B line of FIG. 3;

FIG. 5 is a transversal sectional view showing a dummy-plate portion ofa boat for a thermal process;

FIG. 6 is a view similar to FIG. 4 for explaining an effect that anengaging hole prevents dropping of a supporting plate; and

FIG. 7 is a view similar to FIG. 6 for explaining an effect that adummy-plate engaging hole prevents dropping of a dummy plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an embodiment of the present invention will be describedwith reference to the attached drawings. FIG. 1 is a sectional viewshowing a vertical thermal processing unit according to an embodiment ofthe present invention. FIGS. 2(a) and 2(b) are views showing a boat bodyof a boat for a thermal process. FIG. 3 is a transversal sectional viewshowing a supporting-plate portion of a boat for a thermal process. FIG.4 is an enlarged sectional view taken along a B-B line of FIG. 3. FIG. 5is a transversal sectional view showing a dummy-plate portion of a boatfor a thermal process;

As shown in FIG. 1, the vertical thermal processing unit 1 has areaction tube 2 (processing container) made of quartz, which forms athermal processing furnace for containing an object to be processed suchas a semiconductor wafer W and carrying out a predetermined process suchas a CVD process.

In the embodiment, the reaction tube 2 has a double-tube structure of aninner tube 2 a and an outer tube 2 b, but the reaction tube 2 may have asingle-tube structure of only an outer tube 2 b. In addition, a circularmanifold 5 is hermetically connected to a lower part of the reactiontube 2, the circular manifold 5 having a gas-introducing-pipe portion(gas introducing port) 3 for introducing a process gas or an inert gasfor purge into the reaction tube 2 and a gas-discharging-pipe portion(gas discharging port) 4 for discharging gas from the reaction tube 2.

A pipe of a gas supplying system is connected to thegas-introducing-pipe portion 3. A pipe of a gas discharging systemincluding a vacuum pump and/or a pressure controlling valve or the like,which is capable of reduce and control a pressure in the reaction tube2, is connected to the gas-discharging-pipe portion 4 (omitted in thedrawings). In addition, a cylindrical heater 8 is provided around thereaction tube 2 in such a manner that the inside of the reaction tube 2can be heated and controlled to a predetermined temperature of forexample 300 to 1200° C.

The manifold 5 at the lower end of the reaction tube 2 forms a furnaceopening 6 of the thermal processing furnace. Under the thermalprocessing furnace, a lid 7 that opens and closes the furnace opening 6is provided to be moved up and down by an elevating mechanism 8. The lid7 is adapted to butt against an open end of the manifold 5 tohermetically close the furnace opening 6.

A boat for a thermal process 9 that supports a large number (forexample, about 75 to 100) of large-diameter (for example, 300 mm indiameter) wafers W horizontally in a tier-like manner at intervals in avertical direction is placed on the lid 7 via a heat retaining cylinder10 that is a furnace-opening heat-insulating means. When the lid 7 ismoved up by the elevating mechanism 8, the boat 9 is adapted to beloaded (conveyed) in the reaction tube 2. When the lid 7 is moved down,the boat 9 is adapted to be unloaded (conveyed out) from the reactiontube 2.

On the other hand, as shown in FIGS. 2 to 4, the boat for a thermalprocess 9 has: a plurality of (for example, three) pillars 12 having aplurality of claws 11 formed at predetermined intervals in a heightdirection; and a plurality of supporting plates 13 mounted in atier-like manner via the claws 11 for mounting wafers W. Morespecifically, the boat for a thermal process 9 has a boat body 16consisting of a bottom plate 14, a ceiling plate 15, and the pluralityof pillars 12 extending between the bottom plate 14 and the ceilingplate 15. The supporting plates 13 are supported in a tier-like mannerby the pillars 12 of the boat body 16 via the claws 11. In order to makeuniform a thermal processing condition in the region wherein theplurality of supporting plates 13 occupy, a plurality of (for example, 3to 4) dummy plates 17, as shown in FIG. 5, are supported both on theside of an upper end of the pillars 12 and on the side of a lower endthereof, via the claws 11. The pillars 12 are arranged at predeterminedinterval in a circumferential direction so as to surround the supportingplates 13 and the wafers W. The pillars 12, the bottom plate 14 and theceiling plate 15 are integrally joined by means of welding or the like.

The boat body 16, the supporting plates 13 and the dummy plates 17 maybe made of quartz in a case wherein they are used at a middle highertemperature, for example a thermal processing temperature not higherthan 1000° C. However, it is preferable that they are made of siliconcarbide (SiC) in a case wherein they are used at a relatively highertemperature, for example a thermal processing temperature of about 1050°C. to 1200° C. In the case, in order to prevent that the wafers W arecontaminated by a silicon carbide material whose fineness is low, it ispreferable that a protective film is formed by for example a CVD processonto the boat body 16, the supporting plates 13 and the dummy plates 17,after working process thereof. In addition, the supporting plates 13 andthe dummy plates 17 are formed to substantially the same outer shape.

The ceiling plate 15 and the bottom plate 14 are formed to be circular,respectively. In a case wherein they are used for a thermal process at ahigh temperature, it is preferable to provide a slit 18 in the ceilingplate 15 for causing thermal stress to escape. In addition, in theembodiment, as shown in FIG. 2(a), a cut-out portion 19 for avoidinginterference with a sticklike temperature detector is provided at aperipheral portion of each of the ceiling plate 15 and the bottom plate14.

Regarding the boat body 16, in order to enable attaching and detaching(mounting and removing) of the supporting plates 13 and the dummy plates17 as well as conveying-in and conveying-out of the wafers W in front ofthe boat body 16, the pillars 12 are arranged not in a front regionthereof, but at at least three positions in a left region thereof, aright region thereof and a back region thereof. Four pillars 12 may beused by providing two pillars 12 at left and right positions in the backregion.

In order to support the supporting plates 13 and the dummy plates 17more stably, as shown in FIG. 3, the left and right pillars 12 arearranged a little ahead of a central line La extending in a left-rightdirection of the boat body 16. Then, the horizontal claws 11 are formedat predetermined pitch intervals on the inner sides of the pillars 12.The claws 11 can be formed by making the grooves 20 by whittling theinner sides of the pillars 12 by means of for example a rotary grindingblade which may be inserted through an open side of the boat body 16. Inthe case, it is preferable that the claws 11 are formed to be thin andsmall in order to inhibit thermal capacity of the claws 11 and to makeuniform temperature within the surface of each wafer W.

In addition, a pitch interval Pa of the claws 11 supporting the dummyplates 17 is formed to be smaller than a pitch interval Pa of the claws11 supporting the supporting plates 13, in order to assure a mountingregion of the predetermined number of wafers W in a limited space in theboat body 16 of the boat for a thermal process 9, which is set based ona relationship of the height of the vertical thermal processing unit 1.

Back portions (back surfaces) of the grooves 20 of the left and rightpillars 12 are formed to be in parallel with a central line Lb extendingin a front-back direction of the boat body 16. In addition, a backportion (back surface) of the groove 20 of the back pillar 12 is formedto be in parallel with the central line La in the left-right directionof the boat body 16. Then, as shown in FIG. 3, in outer peripheries ofthe supporting plates 13 and the dummy plates 17, cut-out portions 21 inparallel with the back portions (back surfaces) of the grooves 20 of theleft and right pillars 12 and cut-out portions 22 in parallel with theback portion (back surface) of the groove 20 of the back pillar 12 areformed. Thus, the supporting plates 13 and the dummy plates 17 can besurely and easily mounted onto the boat body 16.

The supporting plate 13 is formed to be circular in such a manner thatan outer diameter thereof is a little larger than that of the circularwafer W in order to support a peripheral portion of the wafer W. Herein,in order to prevent that the reverse surface of the wafer W is damagedand/or that slip by gravity stress is generated in the wafer W, a wafermounting surface (object-to-be-processed mounting surface) 23 of thesupporting plate 13 is mirror ground, and then a minute irregularity(omitted in the drawings) is provided in the wafer mounting surface 23of the supporting plate 13 by means of a surface-roughening process suchas a sand blasting method, in order to inhibit sticking of the wafer W.Alternatively, instead of carrying out both the mirror grinding processand the surface-roughening process, a grinding process aiming at apredetermined desired surface roughness is also effective.

Then, in order to inhibit the phenomenon wherein the wafer W is stuck tothe wafer mounting surface 23 of the supporting plate 13 even at athermal process at a high temperature of for example 1050° C. to 1200°C., grooves 24 and through holes 25 are provided in the wafer mountingsurface 23 of the supporting plate 13. In the embodiment, as shown inFIGS. 3 and 4, a plurality of, for example two, circular concentricgrooves 24 are formed in the wafer mounting surface 23 of the supportingplate 13, and a plurality of through holes 25 vertically piercing thesupporting plate 13 are provided in each groove 24 at predeterminedintervals in a circumferential direction thereof. Although it ispreferable that the plurality of grooves 24 is provided, only one groovemay be provided. In addition, although it is preferable that the groove24 is continuous in the circumferential direction thereof, the groove 24may be formed to be intermittent in the circumferential directionthereof. In addition, although it is preferable that the groove 24 iscircular, the groove 24 may be formed to be radial. Furthermore, thegroove 24 may be formed to be meshy. That is, arrangement and/or shapeof the groove 24 are not limited.

In addition, as shown in FIG. 4, it is preferable that a standing-upwall 26 to prevent dropping of the wafer W is provided in a peripheralportion of the supporting plate 13 to substantially the same height asthe wafer W. However, the standing-up wall 26 may be unnecessary as itis not easy for the wafer W to slide on the wafer mounting surface 23 ofthe supporting plate 13 because of the minute irregularity(surface-roughening process), the grooves 24 and the through holes 25(which cause air remaining between the wafer and the wafer mountingsurface at a wafer mounting to escape).

In addition, stopper members 27 are provided on the supporting plate 13,as a left engaging part and a right engaging part that can be engagedwith claws 11 of the pillars 12 on the left and the right hands in orderto prevent dropping of the supporting plate 13. The stopper members 27project downward from left and right edge portions of the reversesurface of the supporting plate 13, respectively. When the stoppermembers 27 are respectively butted against lateral surfaces on the backside of the left and right claws 11 to be engaged therewith, forwardmovement of the supporting plate 13 is adapted to be blocked. Herein,movement of the supporting plate 13 in a backward direction and in theleft-right direction is blocked by the pillars 12.

In order to inhibit thermal capacity of the stopper members 27 and tomake uniform temperature within the surface of a wafer W, it ispreferable that the stopper members 27 are formed to be thin and small.In addition, because of the same reason, the reverse surface of thesupporting plate 13 is formed to be as flat as possible except for thestopper members 27.

As shown in FIG. 5, similarly to the supporting plate 13, stoppermembers 28 are provided on the dummy plate 17, as a dummy-plate leftengaging part and a dummy-plate right engaging part that can be engagedwith claws 11 of the pillars 12 on the left and the right hands in orderto prevent dropping of the dummy plate 17. Herein, it is preferable thata slit 29 for causing thermal stress to escape is provided in a radialdirection forward from a center of the dummy plate 17 in a case whereinthe dummy plate 17 is used for a thermal process at a high temperature.

According to the above boat for a thermal process 9 or the verticalthermal processing unit 1 using the boat for a thermal process 9, thesupporting plates 13 for mounting the wafers W are mounted in atier-like manner to the plurality of pillars 12 via the claws 11, thepillars 12 having the claws 11 formed at predetermined intervals in aheight direction, and the grooves 24 and the through holes 25 areprovided in the wafer mounting surface 23 of the supporting plate 13.Thus, an air layer is formed between the wafer mounting surface 23 ofthe supporting plate 13 and the wafer W, so that the sticking of thewafer W is inhibited by the air layer. Thus, even at a thermal processat a high temperature, the sticking of the wafer W can be prevented, andgeneration of slip caused by gravity stress partly in the wafer W, whichis caused by the minute irregularity and projections on the wafermounting surface 23, can be inhibited.

In addition, the stopper members 27 that can be engaged with claws 11 ofthe pillars 12 on the left and the right hands to prevent dropping of asupporting plate 13 are provided on the supporting plate 13. Thus, thedropping of the supporting plate 13 caused by vibration or the like canbe prevented. That is, shock-resistance and durability can be improved.In addition, the dummy plates 17 are mounted at the upper end portionand the lower end portion of the pillars 12 via the claws 11, and thestopper members 28 that can be engaged with claws 11 of the pillars 12on the left and the right hands to prevent dropping of a dummy plate 17are provided on the dummy plate 17. Thus, the dropping of the dummyplate 17 caused by vibration or the like can be prevented. That is,shock-resistance and durability can be improved.

If the dummy plate 17 is made of SiC, the dummy plate 17 may be made bymolding. In the case, differently from a dummy wafer made by slicingingot, the stopper members 28 may be easily formed integrally. Inaddition, regarding the boat for a thermal process 9, the boat body 16and the supporting plates 13 are formed separately. Thus, manufacturingthereof, cleaning thereof, replacement of the supporting plates 13, andthe like are easy.

The embodiment of the present invention is explained above in detailwith reference to the drawings. However, the present invention is notlimited to the above embodiment, but may be variously modified orchanged within the substance of the present invention. For example, inorder to facilitate transfer of the wafers W by a transferringmechanism, the supporting plate 13 may be formed into a horseshoe shapewhose front side is open. In addition, a material for the boat body 16,the supporting plates 13 and the dummy plates 17 is preferably siliconcarbide, but may be poly-silicon (Si). The object to be processed may bea LVD substrate or the like, instead of the semiconductor wafer.

Regarding the function of preventing the dropping of the supportingplate 13 and the dummy plate 17, instead of the stopper members 27, 28,engagement holes as shown in FIGS. 6 and 7 may be used.

In the case shown in FIG. 6, on the reverse surface of the supportingplate 13, a left engaging hole 127 that can be engaged with an upperportion of a claw of the pillar on the left hand of the supportingplates 13, a right engaging hole 127′ that can be engaged with an upperportion of a claw of the pillar on the right hand of the supportingplates 13, and a back engaging hole 127″ that can be engaged with anupper portion of a claw of the pillar behind the supporting plates 13are provided to prevent dropping of the supporting plate 13.

Regarding the dummy plate 17, the same structure may be adopted toprevent dropping thereof. That is, as shown in FIG. 7, on the reversesurface of the dummy plate 17, a dummy-plate left engaging hole 128 thatcan be engaged with an upper portion of a claw of the pillar on the lefthand of the dummy plates 17, a dummy-plate right engaging hole 128′ thatcan be engaged with an upper portion of a claw of the pillar on theright hand of the dummy plates 17, and a dummy-plate back engaging hole128″ that can be engaged with an upper portion of a claw of the pillarbehind the dummy plates 17 are provided to prevent dropping of the dummyplate 17.

1. A boat for a thermal process comprising: a plurality of pillars, aplurality of claws formed in each of the pillars in a height directionat predetermined intervals, a plurality of supporting plates mounted ina tier-like manner between the plurality of pillars via the claws, eachsupporting plate having an object-to-be-processed mounting surface onwhich an object to be processed can be mounted, and a groove and athrough hole provided in the object-to-be-processed mounting surface,wherein the plurality of pillars are arranged at least on the left handand on the right hand of the supporting plated, and the supporting platehas a left engaging part that can be engaged with a claw of the pillaron the left hand of the supporting plates in order to prevent droppingof the supporting plate, and a right engaging part that can be engagedwith a claw of the pillar on the right hand of the supporting plates inorder to prevent the dropping of the supporting plate.
 2. A boat for athermal process according to claim 1, wherein a minute irregularity isprovided in the object-to-be-processed mounting surface in order toinhibit sticking of the object to be processed.
 3. A boat for a thermalprocess according to claim 1, wherein the supporting plates aresubstantially circular, and the plurality of pillars are arrangedbehind, on the left hand of, and on the right hand of the supportingplates, perpendicularly to the supporting plates.
 4. A boat for athermal process according to claim 1, wherein the supporting plate issubstantially circular, a plurality of circular grooves areconcentrically provided, and a plurality of through holes are arrangedin each circular groove at predetermined intervals in a circumferentialdirection of the circular groove.
 5. A boat for a thermal processaccording to claim 1, wherein each of the left engaging part and theright engaging part is a stopper member that is abutted against alateral wall part of the claw. 6-13. (Canceled)
 14. A boat for a thermalprocess according to claim 3, wherein the supporting plate has a leftengaging hole that can be engaged with an upper portion of a claw of thepillar on the left hand of the supporting plates, a right engaging holethat can be engaged with an upper portion of a claw of the pillar on theright hand of the supporting plates, and a back engaging hole that canbe engaged with an upper portion of a claw of the pillar behind thesupporting plates.
 15. A boat for a thermal process according to claim1, wherein dummy plates are mounted at an upper end portion and a lowerend portion of the pillars.
 16. A boat for a thermal process accordingto claim 1, wherein a plurality of dummy plates are mounted in atier-like manner between the plurality of pillars via the claws, at anupper end portion and a lower end portion of the pillars, respectively.17. A boat for a thermal process according to claim 16, wherein thedummy plates are substantially circular, and the plurality of pillarsare arranged behind, on the left hand of, and on the right hand of thedummy plates, perpendicularly to the dummy plates.
 18. A boat for athermal process according to claim 17, wherein the dummy plate has adummy-plate left engaging part that can be engaged with a claw of thepillar on the left hand of the dummy plates in order to prevent droppingof the dummy plate, and a dummy-plate right engaging part that can beengaged with a claw of the pillar on the right hand of the dummy platesin order to prevent the dropping of the dummy plate.
 19. A boat for athermal process according to claim 18, wherein each of the dummy-plateleft engaging part and the dummy-plate right engaging part is a stoppermember that is abutted against a lateral wall part of the claw.
 20. Aboat for a thermal process according to claim 17, wherein the dummyplate has a dummy-plate left engaging hole that can be engaged with anupper portion of a claw of the pillar on the left hand of the dummyplates, a dummy-plate right engaging hole that can be engaged with anupper portion of a claw of the pillar on the right hand of the dummyplates, and a dummy-plate back engaging hole that can be engaged with anupper portion of a claw of the pillar behind the dummy plates.
 21. Avertical thermal processing unit comprising: a boat for a thermalprocess according to claim 1, and a thermal processing furnace that cancontain the boat for a thermal process.